This invention relates to a voltage protector, and more particularly, to a voltage protection circuit for a coin changer/validator unit in a vending machine with a multi-drop bus.
Automated coin vending machine manufacturers have adopted a set of standard interconnection protocols that control operations between machine controllers and various credit and money handling units in a vending machine. The standard, available from the National Automatic Merchandising Association, or NAMA, uses the multi-drop bus, or MDB, to connect the components of the vending machine, such as the coin changer/validator, to the machine controller. The bus supplies both power and communications data to the different components from the machine controller, thus allowing different components from different vendors to be interconnected and operate successfully together.
The NAMA voltage standard for the multi-drop bus establishes an acceptable range of voltages that can be supplied to the components of the vending machine without damage. However, the standard does not specify any power conditioning. As a result, spikes that occur on the power lines of the bus, especially when the AC power is suddenly cut off and then restored, can cause significant damage to the components of the vending machine, particularly the coin changer/validator. The internal power sources for the components, such as the coin changer/validator, afford only limited protection, and frequently fail adequately to protect the components against spikes on the power line. In addition, the multi-drop bus power supplies provide inadequate or no spike protection at all for the bus itself.
Accordingly, there is a need for a plug-in voltage protector for a multi-drop bus in a vending machine that can be added to any vending machine and protect the components of the machine from damaging spikes in power.
There is also a need for a voltage protector for a multi-drop bus in a vending machine that protects the multi-drop bus from damaging spikes in power.
There is a still further need for a voltage protector for a multi-drop bus in a vending machine that protects the coin changer/validator from damaging spikes in power.
In accordance with one aspect of the invention, a protective circuit for an electronic device includes two spike prevention circuits for preventing current spikes from flowing to the electronic device. The first spike prevention circuit prevents spikes above a first predetermined voltage from flowing to the electronic device. The second spike prevention circuit is connected in series after the first spike protection circuit and prevents current spikes above a second predetermined voltage from flowing to the electronic device.
In accordance with another aspect of the present invention, a voltage protective circuit for a component connected to a multi-drop bus in a vending machine includes an input terminal for inputting a first voltage from the multi-drop bus, an output terminal for outputting the first voltage to the component, and a line connecting the input and output terminals. Two spike prevention circuits are included in the line. The first spike prevention circuit prevents current spikes above a first predetermined voltage from flowing along the line to the component. The second spike prevention circuit is connected in series after the first spike protection circuit and prevents current spikes above a second predetermined voltage from flowing along the line to the component. The component may be a coin changer/validator in the vending machine.
In accordance with a further aspect of the present invention, a separate, plug-in voltage protector is connected between the DC power source and the multi-drop bus of a vending machine. The voltage protector protects at least one of the components of the vending machine from voltage spikes on the multi-drop bus from the DC power source. The protected component may be a coin changer/validator in the vending machine.